1. Field of the Invention
The present invention relates to lighting apparatus, and more particularly to lighting apparatus having means for controlling the pattern and intensity of the emitted light.
2. Description of the Prior Art
Prior approaches to improving surgical lighting have generally relied on increasing the size of the lighting fixture or the number of light sources. For example, Herold, U.S. Pat. No. 3,927,313 discloses a surgical lighting fixture having several individual light sources evenly arranged around a central axis. A problem with conventional multiple source lightheads however, is that they produce multiple shadows when the beams are interrupted.
Efforts to reduce shadow formation have been made. Brendgord et al., U.S. Pat. No. 4,037,096 which issued on July 19, 1977, discloses a single source lighthead used with a multiple reflector optical system. The light rays are directed by means of the multiple reflectors to approach the illuminated area in an angled relationship relative to the axis of symmetry of the lighting apparatus, rather than parallel to the axis. Because the light rays approach objects from all angles, they tend to travel around the object, thus, reducing shadow formation on the desired area.
Gehly et al., U.S. Pat. No. 4,651,257 issued on Mar. 17, 1987 discloses a multiple lighting apparatus designed to reduce shadows while providing a large field of intense illumination. The light rays projected from the reflector converge at an acute angle relative to the axis of symmetry of the lighting apparatus, crossing that axis, to produce a single beam.
Single source lightheads eliminate the problem of multiple shadows but have not heretofore provided both high intensity and a large pattern of illumination. To achieve the desired intensity, the pattern of illumination must be limited or the wattage of the bulb increased. The achieve a large pattern, the intensity is reduced. Single source surgical lightheads generally offer their best characteristics at a pattern no greater than six inches and an intensity no greater than 6,000 foot candles.
In some applications, for example cardiovascular surgery, a larger pattern of illumination is preferred. In Europe, the trend is to couple larger surgical lights to provide a larger illumination pattern with a smaller light of greater intensity to pinpoint a critical area.
In the specialized lighting utilized for surgical procedures, it is frequently desirable to be able to adjust the pattern size of the light pattern on the wound site depending upon the particular procedure being used and/or the progress of the operation during the surgical procedure.
The conventional means of accomplishing a change in focus and/or a change in pattern size is by mechanical movement of the bulb relative to the reflector or reflectors of the optical system. This normally involves utilization of a lever or levers located on the light itself in order to initiate physical lamp source displacement. Fischer et al., U.S. Pat. No. 4,288,844, issued on Sept. 8, 1981 discloses a means for controlling pattern size and/or focus of surgical lighting. Several commercially available lighting fixtures provide some adjustability by means of altering the position of the entire lighting fixture relative to the work surface or by means of complicated light source positioning.
Gehly et al., U.S. Pat. No. 4,617,619 issued on Oct. 14, 1986 describes a lighting apparatus having a multiple reflector system which permits the pattern and intensity of illumination to be adjusted by rotation of one of the reflectors.
Refractive lenses or filters for focusing light emitted from a lighting apparatus are available. Greppin U.S. Pat. No. 2,280,402 issued on Apr. 21, 1942 describes a dental lamp having a filter with multiple diffusing ribs for spreading the light laterally relative to the optical axis. Gulliksen, U.S. Pat. No. 4,207,607 issued on June 10, 1980 describes a lighting apparatus having a filter with varying zones for controlling or not controlling the direction of the light emitted from the apparatus.
An object of the present invention is to provide a lighting fixture having a sufficient peak illuminance and a useful uniform pattern size to be useful for surgical procedures. It is a further object to the present invention to provide a lighting fixture which eliminates the need for refocusing or repositioning the lighthead when the pattern size is changed. Finally, it is yet another object of the invention to provide a lighting fixture which will produce a variety of pattern sizes without sacrificing other optical characteristics of peak illuminance and depth of field.